On using 'Unread from here' option, it should also be marked as unseen to the sender.
On right click, when the sender chooses the option of 'Unread from here' it is marked as unread only for the viewer and not the sender of the message. It should also be marked as unread for the sender. I know it can be misleading. So this feature should only be available for a limited period of time. Let's say, I received a message and I viewed it by mistake and I don't want to let the other person know or want to reply afterwards with the confirmation that the other person does not feel ignored, I should be able to mark it as unseen within 10 minutes of seeing the message. In this case, it would be marked as unseen for the sender of the message as well.